@gunrunnerjohn posted:One benefit of not having any other devices in series with the LED is you get a lower voltage startup. The nice thing about the two-pin bi-color LED's is the have internal reverse polarity protection based on the two LED chips. Sometimes the K.I.S.S principle works out best.
Yes we are on the same page John. The idea of trying CL2N3's was to see if they offer any great advantage over the KISS approach. The advantage is that from about 7.5 volts up there is no change in LED intensity because the drivers are controlling the current. The downside is the two blocker diodes add to the required start up voltage making it around 6.5 volts. Plus more complexity and cost. Not good. And I proved the blocker diodes are essential. 
In the end I will likely go with a resistor and two LEDs in parallel. I modded one of my 2mm class marker led boards to put the leds in parallel, just for testing. Playing with that a bit I found a startup voltage of about 5.4 gives pretty good intensity. So now I want to test that with a can motor and see if we are in the ballpark. I figure the typical engine can motor voltage range would likely be from about 5vdc (as Bob said) up to about 10vdc. So that's the sweet spot. Research continues. 
